1. Field of the Invention
invention relates generally to an apparatus for recording and/or reproducing a PCM (pulse-code modulated) audio signal by a rotary head, and more particularly is directed to an apparatus for recording an index signal, such as, a signal indicative of a starting point of a recorded event, in an oblique track in a so-called after-recording mode, or for erasing such index signal.
2. Description of the Prior Art
An 8 mm video tape recorder can be used in a normal recording mode in which an audio signal is frequency modulated prior to being mixed with a color video signal and then recorded in such a way that the audio signal can be frequency separated from the color video signal upon playback, and also in an optional recording mode in which the audio signal is pulse-code modulated and recorded in a so-called overscan area which is separate from the main area of each oblique track in which the color video signal is recorded.
As is shown on FIG. 1, a rotary head assembly of the 8 mm video tape recorder includes recording and reproducing rotary magnetic heads HA and HB. These rotary magnetic heads HA and HB have gaps with different azimuth angles and are mounted on a rotary drum 1 with an angular spacing of 180.degree. therebetween. Rotary heads HA and HB are rotated at a rotational speed equal to the standard frame frequency (30 Hz) in the direction indicated by arrow 3H and protrude slightly from the peripheral surface of the rotary drum 1. A magnetic tape 2 is wrapped around the peripheral surface of rotary drum 1 over an angular extent of 221.degree. and is suitably transported at a constant speed in the direction indicated by an arrow 3T.
Accordingly, tracks 4A and 4B, each having a length corresponding to an angular extent of 221.degree. on the surface of drum 1, are alternately formed on tape 2 by rotary heads HA and HB, respectively, as shown in FIG. 2. In a so-called overscan area AP of each track having an angular extent of 36.degree. measured from a point at which the rotary heads HA and HB start scanning the tracks 4A and 4B, there is recorded an audio signal corresponding to one field period of the video signal and which has been pulse-code modulated and time compressed. On the succeeding main area AV of each track having an angular extent of 180.degree., there are recorded a color video signal of one field period, an FM (frequency modulated) audio signal of one field and tracking pilot signals, respectively. The remaining area of each track which has an angular extent of 5.degree. is assigned as a spare area in which the head is disengaged from the tape.
Further, the PCM audio signal can be recorded and reproduced by the 8 mm video tape recorder in a so-called "audio-use" mode in which, as disclosed in detail in U.S. Pat. No. 4,542,419, issued on Sept. 17, 1985 and having an assignee in common herewith, the main recording area AV of each track is also used for recording the PCM audio signal. In such audio-use or multi-PCM mode, the 8 mm video tape recorder becomes a PCM audio signal recording and/or reproducing apparatus in which PCM audio signals can be recorded in multiple channels. More specifically, as shown on FIG. 3, in the audio-use or multi-PCM mode, the area AV of each track corresponding to the angular range of 180.degree. is divided equally by 5 and the PCM audio signal is recorded in a selected one of these divided portions during scanning of each track. Therefore, the whole area of each track shown on FIG. 2, including the area AP and the area AV, is divided into 6 track areas AP1 to AP6, each corresponding to an angular range or extent of 36.degree., and first to sixth track channels are formed by the same numbered segments or track areas AP1 to AP6 of the respective skewed tracks 4A,4B,4A, 4B, etc., shown on FIG. 3, whereby a suitably time compressed PCM audio signal can be recorded in any desired channel. For example, the PCM audio signal may be recorded first in the segments or track areas AP1 of the successive tracks 4A,4B, from one end of the tape to the other. Thereafter, the PCM audio signal may be further recorded in segments or track areas AP2 of the successive tracks from one end of the tape to the other. Accordingly, PCM audio signals can be recorded in and reproduced from each of the six channels with the result that, in the audio-use or multi-PCM mode shown on FIG. 3, the tape 2 has a recording time or capacity six times as long as when a PCM audio signal is recorded only in the overscan area AP of each track, as on FIG. 2.
In the case of the multi-PCM mode, if recording and/or reproducing is effected in or from each segment track area, the PCM signal processing circuit used therefor may be the signal processing circuit provided for processing the PCM audio signal recorded in the single channel constituted by the track areas AP in the prior art 8 mm video tape recorder.
The track format of the above mentioned 8 mm video tape recorder will now be described more fully with reference to FIG. 4, in which contact of the rotary head with the tape 2, that is, the starting point of the track, begins at the right-hand side where there is provided a tracing starting area 11 corresponding, in extent, to a 5.degree. rotation angle of a rotary head. At the rear or trailing portion 12 of tracing starting area 11, a period having an angular range or extent of 2.06.degree. and corresponding to 3H of the video signal, where H is the horizontal period, is assigned as a preamble area which will become a clock run-in area synchronized with the succeeding PCM data. Following clock run-in area 12, there is provided a PCM data recording area 13 having an angular extent of 26.32.degree. and in which a time compressed PCM audio signal is recorded. A postamble area 14 also having an angular extent of 2.06.degree. (3H) follows the PCM data recording area 13 so as to be used as a back margin area to cope with the displacement of the recording position when the recording is carried out in the so-called after-recording mode. A next area 15 having an angular extent of 2.62.degree. is assigned as a guard band area for separating the video signal area 16 which follows from the PCM data area 13. The video recording area 16 has an angular range of 180.degree. as earlier noted for receiving the recorded video signal of one field period. Next to the area 16, there is provided a head disengaging area 17 having an angular extent of 5.degree. and in which the rotary head is disengaged freely from the magnetic tape.
A track format used in the multi-PCM mode will now be described with reference to FIG. 5 in which it is shown that the format for each segment track area for the PCM audio signal is exactly the same as the format for the PCM audio area in the normal 8 mm video tape recorder. Thus, each segment track area in FIG. 5 is formed of a tracing starting area 21, a preamble area 22, a PCM data area 23, a postamble area 24 and a guard band area 25. The same format is assigned to each of the segment track areas AP1 to AP6 on FIG. 3.
Generally, the PCM data is recorded on the tape with the binary code data having a logic level "1" or "0" being modulated to signals of respective frequencies. In the 8 mm video tape recorder, for example, the data having the logic level "1" is modulated to, or represented by a signal having a frequency of 5.8 MHz which is recorded, while the data having the logic level "0" is modulated to, or represented by a signal having a frequency 2.9 MHz which is recorded. In the prior art, only the data having the logic level "1", that is, the signal having the frequency 5.8 MHz, is recorded in each preamble area 12 or 22 and in each postamble area 14 or 24.
A so-called program search method for locating a starting point of a recorded event in the 8 mm video tape recorder mode and the multi-PCM mode has been proposed by a person or persons having a duty of assignment to the assignee of the present application and is described in U.S. patent application Ser. No. 838,626, filed on Mar. 11, 1986. In accordance with such method, an index signal is recorded in, for example, the postamble area 14 or 24 of each track format described above, and this index signal is used to access the starting point of the recorded event on the tape. Moreover, the index signal can be recorded and/or reproduced by the rotary heads so that stationary recording and reproducing heads are not required for the index signal. Further, an area specifying signal for identifying the postamble area as the area receiving the index signal is generated, whereby the index signal can be recorded, or the recorded index signal can be erased, within such area specified by the area specifying signal. When the index signal is to be inserted into or erased from a tape on which the PCM data is already recorded, the user depresses an index signal button when the tape is at a position at which the index signal should be inserted or erased, and the index signal is recorded or erased within the index area during a predetermined time period.
In accordance with the above described earlier proposal, an index signal can be recorded or erased by the rotary head or heads so that a special stationary head for the index signal is not required. Further, since the index signal is recorded in an area separated from the track areas for recording of the PCM data and the video signal, it is possible to insert or erase the index signal in the after-recording mode.
It is further to be noted that, in the 8 mm video tape recorder, the tape speed can be selected to be either a first tape speed for an SP (short play) mode or a second tape speed, which is half the first tape speed, for an LP (long play) mode.
FIGS. 6 and 7 typically illustrate recording track patterns for the SP mode and the LP mode, respectively, at the portions of the tracks near to the PCM areas indicated at AP on FIG. 2. In FIGS. 6 and 7, the hatched areas each represent a postamble area 14 or 24 (FIGS. 5 and 6) into which the index signal is inserted or recorded, that is, the index area. It will be clear from a comparison of FIGS. 6 and 7, that the recording track pitch TP.sub.1 in the LP mode is substantially smaller than the recording track pitch TP.sub.2 in the SP mode.
When the index signal is inserted in the afterrecording mode or erased, the index signal is recorded in, or erased from, the respective area of each track during a predetermined time period as mentioned before, and as indicated by the hatched areas I.sub.A1 and I.sub.A2 on FIGS. 7 and 6, respectively. If the index signal is inserted or recorded in such areas I.sub.A2 and I.sub.A1 during the same time periods in the SP and LP modes, respectively, it will be clear form FIGS. 6 and 7 that the length L.sub.1 along the tape occupied by tracks having the index signal inserted in the LP mode is shorter than, for example, one-half the length L.sub.2 along the tape occupied by tracks having the index signal inserted in the SP mode.
As a result of the above, when the starting point of a recorded event on the slant track is accessed in the high speed search mode and the tape speed used in the high speed search mode is the same whether the event was recorded in the SP mode or in the LP mode, there is the possibility that the rotary heads HA and HB in obliquely scanning the tracks, as shown by arrows S.sub.2 and S.sub.1 on FIGS. 6 and 7, will pick up the index signal in the SP mode, but not in the LP mode.